Prestressing apparatus



June 11, 1968 J. w. HOWLETT 3,337,417

PRESTRESSING APPARATUS Original Filed June 8, 1954 5 Sheets-Sheet 1 ZZmm 3 LL Fig. l

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a '2 58 57 5s INVENTOR. F 52 James W Howlen g- I 1 [Al Anorney June 11,1968 .1. w. HOWLETT 3,387,417

PRESTRESSING APPARATUS Original Filed June 8, 1964 5 Sheets-$heet 2INVENTOR.

James W Hpllefr Attorney June 11, 1968 J. w. HOWLETT 3,387,

PRESTRESS ING APPARATUS Original Filed June 8, 1954 3 Sheets-Sheet 3 F ig. ,2

i. ,./4 '7 "3 b xummml James W Howie" 4/ Attorney United States Patent3,387,417 PREd'lRESSlNG APPARATUS James W. Hewlett, Richmond Annex,Calif., assignor to Hewlett Machine Works, a corporation of CaliforniaOriginal application June 8, 1964, Ser. No. 373,464, new

Patent No. 3,327,380, dated June 27, 1967. Divided and this applicationDec. 9, 1966, Ser. No. 6%,472

7 Claims. (Cl. 52-223) ABSTRACT (BF THE DISCLDSURE Prestressingapparatus for a bearing plate for applying tensioning force to a bearingplate to be applied to concrete or the like to be prestressed andincluding a coupling means for a plurality of buttonhead Wire tendonswhich are individually secured by threaded sleeves in a plurality ofthreaded bores formed in one end face of the coupling means, and asecond tendon secured to the coupling means and extending from anopposite end face thereof in generally end to end relation with the wiretendons.

This invention relates generally to the art of prestressing structuralmaterials such as concrete, steel beams and the like, and moreparticularly is directed to the use of elongated tendons that are placedin a tensioned condition for applying prestressing forces.

This application is a division of application Ser. No. 373,464, filedJune 8, 1964, now US. Patent 3,327,380, for Prestressing Apparatus andMethod.

The use of tensioncd tendon members is well known in the prestressingart, it being the general practice to se cure the tendons at oppositeends to a given structural material and apply compressive prestressingforces to the material by placing the tendons under tension.Prestressing tendons may be broadly classified into the two categoriesof wires and bars. Wire tendons are elongated steel members usuallyhaving a diameter of no longer than about inch, and are available incontinuous lengths in roll form. Wires are relatively easy to handle,may be made of higher tensile strength than bars, and can be arranged inlarge pluralities of coextensive tendons to provide an extremely largecombined tensile strength. In comparison, bar tendons may be severalinches in diameter, and have inherent limitations in their utility.Because bars are relatively inflexible, they are normally limited tolengths of about 80 feet, so that they can be transported byconventional trucks or trains. Also, the large bulk and weight of bartendons makes them often ditlicult to manipulate into their requiredpositions.

in View of the foregoing, it is often preferable that pluralities ofcoextensive wire tendons be used Where tensioning forces are required.Nevertheless, however, it may still be desirable in some situations thata single large diameter bar be secured to the material to beprestressed, rather than having to secure a large number of smallerwires. Accordin ly, it is advantageous to couple a large plurality ofcoextensive wires to single large diameter.

bars, so that the wires extend over substantially the full length of thestructural material and the bars are disposed only at the ends forsecurance to the material.

Herctofore, wire tendons have been coupled and/or secured by means ofbuttonhead protuberances provided integrally at the ends of each tendon,the protuberances being formed by a conventional metal deformationprocess. The wires are extended through holes in various anchor members,with the buttonheads subsequently being formed to bear against tieanchor members. Where large pluralities of coextensive wires arerequired, it has been the practice to assemble these Wires in the shopwith anchor members at each end of the wires, so that the whole "iceassembly becomes a substantially unitary structure which must then betransported to the construction job site.

Heretofore, there has been limited versatility in the use of wiretendons with regard to the ease of fabrication and assembly inon-the-job situations. Also, no ready means have been provided forcoupling wire tendons togcther in end to end relation, or for couplinglarge pluralities of wires together in such a manner that further tendonextensions can readily be added. In addition to this previous limitedversatility in coupling and securing wire tendons, there also has notbeen provided ready means for tensioning and securing the tendons attheir ends, and further enabling ready coupling of additional tendons tothose already mounted and tensioned.

A further limitation of preassembled pluralities of Wire tendons is thatthe anchor member secured to their ends is usually of a relatively largediameter. Consequently, such assembly is limited with respect to thestructures through which it must be strung by the diameter of the anchormember, and difiiculties are presented where tendons must be passedthrough relatively small diameter openings in structural materials.

A need has arisen in view of the above for a more versatile wire tendonprcstressing apparatus, with which it is not necessary to preassemblepluralities of wires but rather which readily enables individual wiresto be strung as desired and then be easily secured to suitable anchoringstructures on the job. Likewise, a need has existed for a wireprestressing apparatus which in general has a broader field of utilitythan has been heretofore atforded, and with particular regard to theability to couple and secure wire tendons, both in pluralities'ofcoextensive wires as individual wires.

Accordingly, an object of the present invention is to provide aprestressing apparatus for utilizing wire tendons with great versatilityin various tensioning arrangements, wherein such wire tendons arereadily coupled or anchored to other members forming a part of thecomplete prestressed structure.

Another object of the invention is to facilitate the use of pluralitiesof coextensively disposed tensioned wire tendons, with particular regardto coupling and securing such pluralities to other tendons or members.

A further object is to provide a prestressing apparatus for applyingtensioning force to wire tendons in a ready and quick manner, and forreadily securing the ends of wire tendons so tensioned to maintain themin the required tensioned condition.

Still another object is to provide novel and improved means for securingthe end of a Wire tendon which does not utilize the conventionalintegrally formed buttonhead protuberance, but rather which employsseparate members that are readily attached to a wire tendon.

The invention possesses other objects and features of advantage, some ofwhich of the foregoing will be set forth in the following description ofthe preferred form of the invention which is illustrated in the drawingsaccompanying and forming part of this specification. It is to beunderstood, however, that variations in the showing made by the saiddrawings and description may be adopted within the scope of theinvention as set forth in the claims.

Referring to said drawings:

FIGURE 1 is a fragmentary plan view, partly in cross section, of a wiretendon and coupling means used in conjunction with the presentinvention.

FIGURE 2 is a fragmentary cross sectional view of two wire tendonscoupled together in accordance with the present invention.

FIGURE 3 is a fragmentary cross sectional view of the instantprestressing apparatus shown with a bearing plate for transmittingtensioning forces to a concrete structure.

FIGURE 4 is a fragmentary cross sectional view with portions broken awayillustrating a plurality of wire tendons coupled to a single largerdiameter tendon.

FIGURE 5 is a cross sectional view along the line 5-5 as shown in FIGURE4.

FIGURE 6 is a cross sectional view showing a plurality of tensioned wiretendons connected to a bearing plate for applying prestressing force toa concrete structure.

FIGURE 7 is a cross sectional view depicting jacking means applying atensioning force to a wire tendon for application to a bearing plate andconcrete structure.

FIGURE 8 is a fragmentary cross sectional view depicting prestressingapparatus used in securing two concrete beams to a concrete column.

FIGURE 9 is a fragmentary cross sectional view illustrating a pluralityof spliced wire tendons forming part of prestressing apparatus used insecuring two concrete beams to a concrete column.

FIGURE 10 is a fragmentary cross sectional view showing a modified formof wire tendon and coupling means from that shown in FIGURE 1.

FIGURE 11 is an end view of the tendon shown in FIGURE 10.

FIGURE 12 is a fragmentary cross sectional view showing another modifiedform of wire tendon and coupling means.

FIGURE 13 is a fragmentary cross section-a1 view of a plurality ofcoextensive wire tendons and a single larger diameter tendon all coupledto another single tendon.

FIGURE 14 is a cross sectional view along the line 14-14 shown in FIGURE13.

Prestressing apparatus embodying the present invention generallycomprises at least one bearing plate 11 for transmitting force to astructural material to be prestressed, such as the concrete structure 12shown in FIG- URE 3, and tensionable tendon means secured to the bearingplate for applying tensioning force thereto. The tendon means includes afirst elongated tendon, such as the wire tendon 13 shown in FIGURE 2;means defining a proturberance secured adjacent the end 14 of the tendon13, such as the integrally formed buttonhead 16; an externally threadedtubular sleeve member 17 disposed concentrically on the tendon 13adjacent the protuberance for abutting engagement therewith; a couplingmember having an internally threaded bore threadedly engaging the sleevemember 17, such as the internally threaded tubular member 18; and asecond elongated tendon 19 secured to the coupling member and disposedin general end to end relation with the tendon.

A basic element of the instant prestressing apparatus is a wire tendon21 as shown in FIGURE 1, having protuberances such as the integralbuttonheads 22 and 23 formed at either end of the tendon. An externallythreaded sleeve member 24 can be mounted on the tendon prior toformation of the buttonhead, whereby the sleeve 24 is adapted to engagethe buttonhead 22 in abutting relation. In some instances, it may bedesirable to mount the sleeve members after the buttonhead has beenformed, and for this purpose a split sleeve 26 is provided whichincludes half-tubular segments 27 and 28 as shown in FIGURE 1. The splitsleeve 26 is of particular utility in on the job situations where it isnecessary to couple or secure an existing buttonhead tendon that doesnot already have a sleeve 24. The segments 27 and 28, when placedtogether on a tendon, form the equivalent of a sleeve 24.

In order to couple together two tendons disposed in generally alignedend to end relation, the internally threaded tubular coupler shown inFIGURE 2 can be used in conjunction with a pair of tendons each havingbuttonhead protuberances on their confronting ends. Thus, the wiretendon 19 is provided with a buttonhead 29 and a sleeve member 3-1, sothat the coupler 18 threadedly engages both sleeves 17 and 31 therebyconnecting the wire 13 and 19.

Means for securing a single wire tendon in a desired tensioned conditionis disclosed in FIGURE 3, and in this regard it is noted that thebearing plate 11 is provided with a hole 32 through which passes the endportion of a wire tendon 33. An elongated externally threaded sleevemember- 34 is concentrically mounted on the tendon 33, and abuttinglyengages a buttonhead 36 on the end of the tendon. The sleeve 34 passesthrough the hole 32, and an internally threaded member such as a nut 37is mounted on the sleeve for axial adjustment thereon. Tensioning meansto be described pull the sleeve 34 outwardly to place the tendon 33under tension, and the nut 37 is then screwed down into abuttingengagement with the bearing plate to maintain the tendon in itstensioned condition. It is noted that the other end of the tendon 33 issuitably anchored to the concrete structure 12, so that when the tendonis tensioned a compressive prestressing force is applied to theconcrete. I11 the event that another tendon 38 is required to be coupledto the tendon 33, a tubular coupler 39 can be used in the same manner asdescribed with regard to FIGURE 2.

In some instances as noted hereinabove, it is advantageous to use aplurality of coextensive wire tendons to achieve extremely high tensileforces, as compared to a single bar tendon of relatively large diameter.As noted, wire tendons can be provided more readily in longer lengthsthan large diameter bars or rods, and are more readily handled. Insituations to be described, it is sometimes desirable to couple a largeplurality of coextensive wire tendons to a single larger diameter bartendon, and in this regard reference is made to FIGURE 4 whereincoupling means in accordance with the present invention is provided forjoining four wires 41 to a single bar tendon 42. In more detail, each ofthe wires 41 has a buttonhead 43 and a sleeve 44 similar to thatdescribed in FIG- URE 1. A coupler member 46 is provided with acorresponding number of internally threaded bores 47 which threadedlyengage the sleeves 44, thus securing the tendons 41 to the coupler 46.The bar 42 can be secured to the opposite face of the coupler 46 by anysuitable means, which as shown may comprise a unidirectional,self-actuated, wedge grip coupling means of the type disclosed in PatentNo. 2,930,642. The bar 42, of course, may be provided with conventionalthreads, which would engage a complimentarily threaded bore in thecoupler 46.

In FIGURE 6, there is shown a prestressing apparatus somewhat similar toa conventional system. A plurality of wire tendons 48, havingbuttonheads 49, pass through holes 51 in a bearing plate 52 whichengages a concrete member 53. The wires 48 also pass through holes 54 inan anchor member 56, with the buttonheads 49 being disposed on the outerside of the anchor member. As in the conventional system, the anchormember 48 can be grasped by suitable jacking means, whereby the wiresare placed under tension, and then shim members such as the two metalplates 57 are interposed between the anchor 56 and bearing plate 52. Inaddition to the structure as described thus far, which is conventional,the instant apparatus provides a plurality of externally threaded sleevemembers 58 on each of the wires 48 tor engagement with their respectivebuttonheads 49. Consequently, it is possible with the instant apparatusto readily couple additional wire tendons in end to end relation withthe wires 48, in the manner already described with regard to FIG- URES 2and 3.

A jack 61 is disclosed in FIGURE 7 for use in applying tension toindividual wire tendons having buttonheads. As shown, the jack 61includes a supporting member 62 having a pair of spider leg members 63which extend into abutting engagement with a bearing plate 64. Aconventional hydraulic means 66 is mounted on the member 62, and has apiston 67 extending axially between the legs 63 and adapted forselective reciprocating movement. A wire tendon 68 extends through thebearing plate, and has a sleeve member 69 engaging a buttonhead '71. Atubular coupler 72 has internal threads which engage the sleeve 69, andexternal threads on which is mounted an internally threaded stop membersuch as the nut 73. The piston 67 of the jack 61 is externally threadedfor engagement with the coupler 72, whereby the jack can be operated topull the wire 68 into a tensioned condition. A tubular shim member 74 isinterposed between the nut 73 and the bearing plate, and when the wireis tensioned to the desired amount the nut 73 is tightened against theshim 74 to maintain the wire in its tensioned condition. It will beappreciated that the jack 61 may also be used to apply tension to thewire 33 as shown in FIGURE 3, the piston 67 engaging the coupler 39 inthe same manner, as described with regard to FIGURE 7.

One use of wire tendons in accordance with the present invention isdisclosed in FIGURE 8, wherein a pair of concrete beams 76 and 77 aresecured to a concrete column 78. In this structure, a plurality of wiretendons 79 are coupled to a single bar 81 by means of a coupler 82 ofthe type described hereinabove with reference to FIGURES 4 and 5. Thebeam 76 is first secured to the column 79 by extending the bar 81through a bore 83 in the column, and then anchoring the bar by means ofa temporary anchor nut 84. The nut 84 may be a wedge grip nut of thetype disclosed in my copending patent application for ConcretePrestressing Apparatus, Ser. No. 302,628, filed Aug. 16, 1963. After thebeam 76 and column 7 8 are secured as shown, the second beam 77 can beconnected by means of another coupler 86 which joins the bar 81 toanother plurality of wire tendons 87.

In FIGURE 9, a pair of concrete beams 88 and 89 are secured to a column91, by means of a plurality of spliced wire tendons 92 which are joinedtogether by means of couplers 93 in the manner described hereinabovewith reference to FIGURES 2 and 3. The individual wires can be strungthrough openings in the beams and columns as shown, which openings neednot be any larger than necessary to accommodate only the wires. It isnot necessary to pass any anchor members through these holes, since thewires can be secured to bearing plates (not shown) in the mannerdescribed above with reference to FIGURE 3. That is, the wires cansimply be passed through the holes in the bearing plates, after whichthe stop nuts 37 are mounted on corresponding sleeve members.

An alternative embodiment regarding the buttonhead protuberances for thewire tendons is disclosed in FIG- URES 10 and 11. In particular, insteadof the integrally formed buttonhead as described hereinabove withreference to FIGURE 1, there is shown in FIGURES 10 and 11 a separateinner tubular member 94 mounted concentrically on a wire tendon 96, andwhich has a tapered outer surface 97. The member 94 is adapted to applyradially inward force on the wire 96, and in this regard is providedwith 'a longitudinal slit 98. The inner bore surface 99 of the member 94is preferably provided with a serrated finish so that it will grip thewire and restrain relative axial movement between the wire and member94. An externally threaded sleeve member 101 is mounted concentricallyon the wire, and has a tapered inner surface 102 which complementarilyengages the tapered surface 97 of the member 94. Thus, as the sleeve 101is urged toward the end of the wire 96, the tapered surfaces create aradially inward force on the inner member 94, which therefore securelygrips the wire. In the embodiment just described the inner diameter ofthe member 94 is dimensioned to form a slight interference fit with thewire 96, so that there will be an initial grip between the wire andmember 94. Another alternative embodiment is disclosed in FIGURE 12,similar to that of FIGURES 10 and 11, but wherein the inner member 94ais not dimensioned for an interference fit with the wire 96. Rather, theend of the wire is peened over by a hammer or the like to provide aslight protuberance 103,, which serves to create the initial gripbetween the member 94a and the wire.

Where large pluralities of coextensive wires are used to provide tensileforces, it has been found that prior to application of tension to thewires they tend to sag or drape irregularly between the points at whichthey are supported. A somewhat better natural drape is obtained with abar. A modified coupler 104 is disclosed in FIG- URES 13 and 14,somewhat similar to the coupler 46 as shown in FIGURE 4, but whichcombines the greater tensile strength of wire tendons with the improvednatural drape of a bar. More particularly, a plurality of internallythreaded bores 106 are disposed in circumferentially spaced relation onone end face of the coupler 104, these bores threadedly engaging sleeveson wire tendons 107 in the same manner as described with regard toFIGURE 4. A larger internally threaded bore 108 is disposedconcentrically within the smaller bores 106, and engages the threadedend 109 of a bar 111 which is of substantially larger diameter than thewires 107. An internally threaded bore 112 is provided on the oppositeend of the coupler 104, and engages the threaded end of another bar 113.The combined tensile strength of the wires 107 and bar 111 issubstantially equal to that of the larger diameter bar 113. Theadvantage of the coupled tendon structure as just described is that thecenter bar 111 controls the desired sag while utilizing the plurality ofwires to achieve the necessary tensile strength. It should be noted thatthe bars 111 and 113 can be secured to the coupler 104 by means of wedgegrip coupling means such as shown in FIGURE 4, instead of theconventional threaded arrange ment as just described.

It will be appreciated from the foregoing that the instant prestressingapparatus affords great versatility in providing tensioning forces forprestressing structural materials. Although the multiwire couplerillustrated in FIGURE 4 shows only four coextensive wire tendons, thesame basic structure has been employed to couple as many as 64 A" wirestogether, it being necessary to use a 2 /2" diameter bar on the otherside of the coupler, whereby the combined strength of the wires wassufficient to hold 650,000 pounds of tensile force. In addition, it is asimple operation with the instant apparatus to couple wire tendons inend to end relation, thus enabling construction of new concrete or otherprestressed structures in adjacent position to previously formedstructures. It is furthermore possible to make on the job assemblies ofthe instant wire tendons, rather than having to preassemble groups ofcoextensive wires at the factory prior to shipment to the constructionsite.

An important feature of the type of coupling as illustrated in FIGURES 4and 13 is that each end of the coupler may be desgined and machined toattach the type or types of tendon or tendons to be connected theretowithout regard for the type or types of tendons to be connected to theopposite end of the coupler. This greatly assists in the economicmanufacture of the coupling, and the best utilization of material toattain a coupler of requisite strength in a minimum overall size.

I claim:

1. Prestressing apparatus comprising, in combination, at least onebearing plate for transmitting force to a material to be prestressed,and tensionable tendon means and means engaging said bearing plate forapplying such force, said tendon means including a plurality ofgenerally coextensive wire tendons each having means defining aprotuberance secured adjacent one end thereof, a plurality of externallythreaded tubular sleeve members one each disposed concentrically on oneeach of said tendons in abutting relation to the protuberance thereon, acoupling member having a plurality of internally threaded bores arrangedin spaced parallel side by side relation and opening to one end face ofsaid coupling member and each being dimensioned to receive one of saidprotuberances and sleeve members, one each of said tendons extendinginto one each of said bores with its corresponding protuberancepositioned internally of said bore and with said sleeve member thereonthreadably engaged with the wall of said bore so as to retain saidprotuberance therein, and a second elongated tendon secured to saidcoupling member and extending from an opposite end face thereof ingenerally end to end relation with said wire tendons.

2. Prestressing apparatus as described in claim 1 wherein said couplingmember is formed with a second bore opening to said opposite end faceand having an axis substantially parallel to said first named bores,said second tendon being a bar tendon having a tensile strengthsubstantially equal to the combined tensile strength of said wiretendons and having one end mounted in said second bore, andunidirectional self-actuated wedge gripping means mounted in said secondbore and securing said bar tendon therein against withdrawal.

3. Prestressing apparatus as described in claim 1 wherein said secondelongated tendon comprises a plurality of second wire tendons havingprotuberances adjacent one end thereof, a plurality of second externallythreaded tubular sleeve members one each disposed concentrically on oneeach of said second tendons in abutting relation to the protuberancethereon, said coupling member having a plurality of second internallythreaded bores arranged in spaced parallel side by side relation andopening to said opposite end face and each being dimensioned to receiveone of the protuberances and sleeve members on said second wire tendons,and one each of said second tendons extending into one each of saidsecond bores with its corresponding protuberance positioned internallyof said second bore and with said sleeve member thereon threadablyengaged with the wall of said second bore so as to retain the abuttingprotuberance therein.

4. Prestressing apparatus as described in claim 1 wherein at least oneof said sleeve members comprises at least two separate segmental tubularmembers externally threaded to form a substantially unitary externallythreaded sleeve when mounted concentrically on one of said wire tendons.

5. Apparatus as described in claim 1 further including a third elongatedtendon disposed generally coextensive with said plurality of tendons andhaving a larger cross sectional area than each one of said plurality,said third tendon being secured to said coupler member in generally endto end relation with said second tendon and with said plurality oftendons being disposed in generally concentric surrounding relation withsaid third tendon.

6 Apparatus as described in claim 1 wherein said means defining at leastone of said protuberances includes an inner generally tubular memberconcentrically mounted on its corresponding tnedon and having an innersurface adapted to grippingly engage said latter tendon to preventrelative axial movement between said latter tendon and inner tubularmember, said inner tubular member being adapted to be urged radiallyinwardly against said tendon and having a tapered outer surface, saidexternally threaded sleeve member for said corresponding tendon havingan internal tapered surface complementarily engaging said outer taperedsurface for bearing radially inwardly on said inner tubular member whensaid sleeve is moved toward the proximate end of said tendon.

7. Apparatus as described in claim 6 wherein said inner tubular memberhas a longitudinal slot therein, and wherein the adjacent end of saidcorresponding tendon is provided with an enlarged portion axiallyengaging said inner tubular member.

References flied UNITED STATES PATENTS 1,909,332 5/1933 Blackburn 522232,728,978 1/1956 Birkenmaier et al. 52230 3,029,490 4/1962 Middendore52223 3,060,639 10/1962 Fields 52223 3,089,215 5/1963 Stubbs 522233,156,071 10/1964 Bijilevelt 52223 FOREIGN PATENTS 222,864 1/ 1962Austria.

511,407 5/1952 Belgium.

940,799 11/ 1963 Great Britain. 1,330,787 5/1963 France.

FRANK L. ABBOTT, Primary Examiner.

JAMES L. RIDGILL, JR., Examiner.

